Alexandre G. Oliveira

IL-6 and IL-10 Anti-Inflammatory Activity Links Exercise to Hypothalamic Insulin and Leptin Sensitivity through IKKβ and ER Stress Inhibition

Physical activity confers beneficial metabolic effects by inducing anti-inflammatory activity in the hypothalamus region of the brain in rodents, resulting in a reorganization of the set point of nutritional balance and reduced insulin and leptin resistance.

Physical exercise reduces circulating lipopolysaccharide and TLR4 activation and improves insulin signaling in tissues of DIO rats.

OBJECTIVE Insulin resistance in diet-induced obesity (DIO) is associated with a chronic systemic low-grade inflammation, and Toll–like receptor 4 (TLR4) plays an important role in the link among insulin resistance, inflammation, and obesity. The current study aimed to analyze the effect of exercise on TLR4 expression and activation in obese rats and its consequences on insulin sensitivity and signaling. RESEARCH DESIGN AND METHODS The effect of chronic and acute exercise was investigated on insulin sensitivity, insulin signaling, TLR4 activation, c-Jun NH2-terminal kinase (JNK) and IκB kinase (IKKβ) activity, and lipopolysaccharide (LPS) serum levels in tissues of DIO rats. RESULTS The results showed that chronic exercise reduced TLR4 mRNA and protein expression in liver, muscle, and adipose tissue. However, both acute and chronic exercise blunted TLR4 signaling in these tissues, including a reduction in JNK and IKKβ phosphorylation and IRS-1 serine 307 phosphorylation, and, in parallel, improved insulin-induced IR, IRS-1 tyrosine phosphorylation, and Akt serine phosphorylation, and reduced LPS serum levels. CONCLUSIONS Our results show that physical exercise in DIO rats, both acute and chronic, induces an important suppression in the TLR4 signaling pathway in the liver, muscle, and adipose tissue, reduces LPS serum levels, and improves insulin signaling and sensitivity. These data provide considerable progress in our understanding of the molecular events that link physical exercise to an improvement in inflammation and insulin resistance.

Hepatocyte Growth Factor Plays a Key Role in Insulin Resistance-Associated Compensatory Mechanisms

Insulin resistance is present in obesity and in type 2 diabetes and is associated with islet cell hyperplasia and hyperinsulinemia, but the driving forces behind this compensatory mechanism are incompletely understood. Previous data have suggested the involvement of an unknown circulating insulin resistance-related β-cell growth factor. In this context, looking for candidates to be a circulating factor, we realized that hepatocyte growth factor (HGF) is a strong candidate as a link between insulin resistance and increased mass of islets/hyperinsulinemia. Our approach aimed to show a possible cause-effect relationship between increase in circulating HGF levels and compensatory islet hyperplasia/hyperinsulinemia by showing the strength of the association, whether or not is a dose-dependent response, the temporality, consistency, plausibility, and reversibility of the association. In this regard, our data showed: 1) a strong and consistent correlation between HGF and the compensatory mechanism in three animal models of insulin resistance; 2) HGF increases β-cell mass in a dose-dependent manner; 3) blocking HGF shuts down the compensatory mechanisms; and 4) an increase in HGF levels seems to precede the compensatory response associated with insulin resistance, indicating that these events occur in a sequential mode. Additionally, blockages of HGF receptor (Met) worsen the impaired insulin-induced insulin signaling in liver of diet-induced obesity rats. Overall, our data indicate that HGF is a growth factor playing a key role in islet mass increase and hyperinsulinemia in diet-induced obesity rats and suggest that the HGF-Met axis may have a role on insulin signaling in the liver.

Double-Stranded RNA-Activated Protein Kinase Is a Key Modulator of Insulin Sensitivity in Physiological Conditions and in Obesity in Mice

The molecular integration of nutrient- and pathogen-sensing pathways has become of great interest in understanding the mechanisms of insulin resistance in obesity. The double-stranded RNA-dependent protein kinase (PKR) is one candidate molecule that may provide cross talk between inflammatory and metabolic signaling. The present study was performed to determine, first, the role of PKR in modulating insulin action and glucose metabolism in physiological situations, and second, the role of PKR in insulin resistance in obese mice. We used Pkr(-/-) and Pkr(+/+) mice to investigate the role of PKR in modulating insulin sensitivity, glucose metabolism, and insulin signaling in liver, muscle, and adipose tissue in response to a high-fat diet. Our data show that in lean Pkr(-/-) mice, there is an improvement in insulin sensitivity, and in glucose tolerance, and a reduction in fasting blood glucose, probably related to a decrease in protein phosphatase 2A activity and a parallel increase in insulin-induced thymoma viral oncogene-1 (Akt) phosphorylation. PKR is activated in tissues of obese mice and can induce insulin resistance by directly binding to and inducing insulin receptor substrate (IRS)-1 serine307 phosphorylation or indirectly through modulation of c-Jun N-terminal kinase and inhibitor of κB kinase β. Pkr(-/-) mice were protected from high-fat diet-induced insulin resistance and glucose intolerance and showed improved insulin signaling associated with a reduction in c-Jun N-terminal kinase and inhibitor of κB kinase β phosphorylation in insulin-sensitive tissues. PKR may have a role in insulin sensitivity under normal physiological conditions, probably by modulating protein phosphatase 2A activity and serine-threonine kinase phosphorylation, and certainly, this kinase may represent a central mechanism for the integration of pathogen response and innate immunity with insulin action and metabolic pathways that are critical in obesity.

Diacerhein Improves Glucose Tolerance and Insulin Sensitivity in Mice on a High-Fat Diet

Obesity and type 2 diabetes are characterized by insulin resistance, and the common basis of these events is a chronic and systemic inflammatory process marked by the activation of the c-Jun N-terminal kinase (JNK) and inhibitor-κB kinase (IKKβ)/nuclear factor-κB (NFκB) pathways, up-regulated cytokine synthesis, and endoplasmic reticulum dysfunction. The aim of this study was to evaluate the effects of diacerhein administration, an antiinflammatory drug that reduces the levels of inflammatory cytokines, on insulin sensitivity and signaling in diet-induced obese (DIO) mice. Swiss mice were fed with conventional chow (control group) or a high-fat diet (DIO group). Later, DIO mice were randomly subdivided into a new subgroup (DAR) that received 20 mg/kg diacerhein for 10 d. Western blotting was used to quantify the expression and phosphorylation of insulin receptor, insulin receptor substrate 1, and Akt and of inflammatory mediators that modulate insulin signaling in a negative manner (IKKβ, JNK, and inducible nitric oxide synthase). We show here, for the first time, that the administration of diacerhein in DIO mice improved endoplasmic reticulum stress, reduced JNK and IKKβ phosphorylation, and resulted in a marked improvement in fasting glucose, a decrease in macrophage infiltration in adipose tissue, and a reduced expression and activity of proinflammatory mediators accompanied by an improvement in the insulin signaling mainly in the liver and adipose tissue. Taken together, these results indicate that diacerhein treatment improves insulin sensitivity in obesity, mediated by the reversal of subclinical inflammation, and that this drug may be an alternative therapy for insulin resistance.

Exercise Intensity, Inflammatory Signaling, and Insulin Resistance in Obese Rats

PURPOSE To evaluate the effects of intensity of exercise on insulin resistance and the expression of inflammatory proteins in the skeletal muscle of diet-induced obese (DIO) rats after a single bout of exercise. METHODS In the first exercise protocol, the rats swam for two 3-h bouts, separated by a 45-min rest period (with 6 h in duration--O + EXE), and in the second protocol, the rats were exercised with 45 min of swimming at 70% of the maximal lactate steady state--SS (DIO + MLSS). RESULTS Our data demonstrated that both protocols of exercise increased insulin sensitivity and increased insulin-stimulated tyrosine phosphorylation of insulin receptor and insulin receptor substrate 1 and serine phosphorylation of protein kinase B in the muscle of DIO rats by the same magnitude. In parallel, both exercise protocols also reduced protein tyrosine phosphatase 1B activity and insulin receptor substrate 1 serine phosphorylation, with concomitant reduction in c-jun N-terminal kinase and IJB kinase activities in the muscle of DIO rats in a similar fashion. CONCLUSIONS Thus, our data demonstrate that either exercise protocols with low intensity and high volume or exercise with moderate intensity and low volume represents different strategies to restore insulin sensitivity with the same efficacy.

Acute exercise induces a phenotypic switch in adipose tissue macrophage polarization in diet‐induced obese rats

It has become clear that exercise may be a useful therapy in the insulin resistance treatment, as it has anti‐inflammatory effects and improves insulin sensitivity. However, it remains uncertain whether exercise affects the adipocytes or infiltrated macrophages. Thus, the aim was to investigate the effects of acute exercise on the inflammatory status and insulin signaling of the white adipose tissue (WAT) fractions (stromal‐vascular fraction [SVF] and adipocytes).

Modulation of double-stranded RNA-activated protein kinase in insulin sensitive tissues of obese humans

Objective: The double‐stranded RNA‐dependent protein kinase (PKR) was recently implicated in regulating molecular integration of nutrient‐ and pathogen‐sensing pathways in obese mice. However, its modulation in human tissues in situations of insulin resistance has not been investigated. The present study was performed to first determine the tissue expression and phosphorylation levels of PKR in the liver, muscle, and adipose tissue in obese humans, and also the modulation of this protein in the adipose tissue of obese patients after bariatric surgery.

Insulin-Resistance-Associated Compensatory Mechanisms of Pancreatic Beta Cells: A Current Opinion

In obesity and in most situations of insulin-resistance, β-cells compensate for this hormonal resistance for long periods of time by an increase in secretory capacity and in β-cell mass. In animal models of insulin-resistance there is islet hyperplasia (1–3) and very recently a clear correlation between BMI and β-cells mass was shown in humans (4). The driving forces that can contribute to the increased β-cell mass in insulin-resistant states are not completely understood. It is well-established that glucose itself is able to induce β-cell hyperplasia (3, 5). However in many situations of insulin-resistance the hyperplastic response comes prior to any change in circulating glucose levels, indicating that other factors independent of glucose may contribute to the islet hyperplasia. Among circulating hormones and/or growth factors such as growth hormone (GH), insulin-like growth factor I (IGF-I), prolactin, and placental lactogen were implicated in islet hyperplasia associated with insulin-resistance. However, some data does not support the contribution of these hormones in islet hyperplasia. For example, GH and IGF-I were not altered in diet-induced obesity (DIO) mice and most insulin-resistant animal models investigated were male, making prolactin and the placental lactogen improbable candidates. In the past 4 years a novel pathway involving a neural relay and two hormones – betatrophin and hepatocyte growth factor (HGF) – were implicated as an inter-organ communication system associated to the compensatory response of β cells in face of insulin-resistance (6–8). In this commentary we will focus on evidence showing the role of this novel pathway in islet hypertrophy associated with obesity and insulin-resistance. In a recent publication by Yi and collaborators (8), the authors identified betatrophin, a novel hormone that increases in insulin-resistant states and controls pancreatic β cell proliferation. This hormone was recognized through the infusion in mice of the insulin receptor antagonist (S961) able to induce insulin-resistance, and also provoke at a dose-dependent manner a dramatic pancreatic β cell proliferation. By microarray, they identified the hormone betatrophin from the liver and adipose tissue of these animals, which showed that it is able to induce beta cell proliferation. In addition, the authors also demonstrated that the betatrophin mRNA was increased in the liver from ob/ob and db/db mice (three to four-fold), as well as during the mice pregnancy (∼20-fold). As discussed below, HGF is a growth factor that plays a key role in regulation of islet mass increases along with hyperinsulinemia in animal models of insulin-resistance, therefore could also play a role, however, this possibility was not addressed by Yi et al. (8). Additional aspects of the work deserve further clarification, although Yi et al. showed a possible cause-effect relationship between betatrophin and an increase in pancreatic β cell proliferation in their approach, some aspects were not thoroughly clarified. For example, they did not demonstrate the correlation between circulating levels of betatrophin and the increase in islet mass; most of the experiments are in an artificial model of insulin-resistance, based on the use of an insulin receptor antagonist, and not in the traditional models of obesity and or insulin-resistance, mainly based on a diet-induced obesity (9, 10); and, the increase in mRNA of betatrophin is much higher in pregnancy than in ob/ob and db/db mice, but the increase in islet mass is usually higher in these genetic models compared to pregnancy (1, 11). In addition, the regulations of complex processes that are evolutionary conserved and/or adaptive traits, such as insulin-resistance is usually involve redundant mechanisms. In this regard, an important point we would like to emphasize is that the compensatory increase in islet cell mass and hyperinsulinemia is multifactorial and involves central nervous system (CNS) (7), and at least one more growth factor besides betatrophin, this one known as HGF, as we previously demonstrated (6). Imai and coworkers identified a neuronal relay, originating in the liver, which enhances both insulin secretion and pancreatic β-cell proliferation (7). They showed that blocking this neural relay in rodent obesity models led to an inhibition in pancreatic islet expansion during obesity development, presenting this inter-organ communication system to be physiologically involved in compensatory β-cell proliferation. This neuronal relay is connected with signaling pathways in the liver, since it is triggered by an increase in the phosphorylation of hepatic extracellular signal-regulated kinase (ERK), which is known to be activated in the liver of a murine obesity model (12). Thus, through an adenoviral gene transduction approach that promoted a liver-selective expression of a constitutively active mutant of mitogen-activated protein kinase/ERK kinase (MEK-1), they were able to induce insulin hypersecretion and β-cell proliferation. Moreover, they also demonstrated that these pancreatic effects of hepatic ERK activation were inhibited by splanchnic afferent blockade, pancreatic vagus dissection, or midbrain transection (7). Kahns group has consistently showed that circulating growth factors, probably produced by the liver, are also important in the connection between insulin-resistance and the increase in islet mass (1, 2). Also, our group recently published a study (6) that presented the HGF as one of the systemic liver-derived growth factors that plays a role in insulin-resistance compensatory mechanism through the liver-to-pancreas axis in the adaptive β cell growth response. The concept of the study, initially, was that since it is well-established that the HGF is a mesenchymal-derived pleiotropic cytokine that regulates cell proliferation, anti-apoptosis, motility, and morphogenesis, suggests that HGF may be a good candidate of circulating insulin-resistance-related β-cell growth factor. Moreover, HGF has at least four characteristics that suggest a pathophysiological link between insulin-resistance and islet hyperplasia/hyperinsulinemia: (1) HGF is mainly produced by the liver; (2) it is under the regulation of the ERK pathway; (3) HGF stimulates insulin secretion and increased islet mass both in vitro and in vivo; and (4) circulating levels are elevated in obesity associated-insulin-resistance. Based on this circumstantial evidence, we studied the role of HGF in insulin-resistance compensatory mechanisms. Our approach aimed to show a possible causal relationship between an increase in circulating HGF levels and compensatory islet hyperplasia/hiperinsulinemia. In this sense, we investigated the association in a dose-dependent, longitudinal approach. Our findings showed the following: (1) there is a strong and consistent correlation between HGF and the compensatory mechanism from β-cells in three animal models of insulin-resistance; (2) that HGF increases β-cell mass in a dose-dependent manner; (3) blocking HGF shuts down the compensatory mechanisms; and (4) an increase in HGF levels seems to precede the compensatory response associated with insulin-resistance, indicating that these events occur in a causal fashion. Additionally, blockages of HGF receptor (Met) worsen the already impaired insulin-induced insulin signaling in the liver of diet-induced obesity rats. In conclusion, it is important to emphasize that the recently described betatrophin is a hormone that has an important role in the connection between insulin-resistance and increased β-cell mass, but other growth factors such as HGF and also neural circuits certainly play an important role in this process (Figure ​(Figure1).1). The contribution of each of these factors in different situations of insulin-resistance, such as in pregnancy, obesity, and type 2 diabetes, deserves further investigation. Figure 1 Schematic representation of the effects of betatrophin and HGF hormones, as well as, neural circuits on islets in which these components together induce the compensatory response to insulin-resistance.

Chlorella modulates insulin signaling pathway and prevents high-fat diet-induced insulin resistance in mice

AIMS The search for natural agents that minimize obesity-associated disorders is receiving special attention. In this regard, the present study aimed to evaluate the prophylactic effect of Chlorella vulgaris (CV) on body weight, lipid profile, blood glucose and insulin signaling in liver, skeletal muscle and adipose tissue of diet-induced obese mice. MAIN METHODS Balb/C mice were fed either with standard rodent chow diet or high-fat diet (HFD) and received concomitant treatment with CV for 12 consecutive weeks. Triglyceride, free fatty acid, total cholesterol and fractions of cholesterol were measured using commercial assay. Insulin and leptin levels were determined by enzyme-linked immunosorbent assay (ELISA). Insulin and glucose tolerance tests were performed. The expression and phosphorylation of IRβ, IRS-1 and Akt were determined by Western blot analyses. KEY FINDINGS Herein we demonstrate for the first time in the literature that prevention by CV of high-fat diet-induced insulin resistance in obese mice, as shown by increased glucose and insulin tolerance, is in part due to the improvement in the insulin signaling pathway at its main target tissues, by increasing the phosphorylation levels of proteins such as IR, IRS-1 and Akt. In parallel, the lower phosphorylation levels of IRS-1(ser307) were observed in obese mice. We also found that CV administration prevents high-fat diet-induced dyslipidemia by reducing triglyceride, cholesterol and free fatty acid levels. SIGNIFICANCE We propose that the modulatory effect of CV treatment preventing the deleterious effects induced by high-fat diet is a good indicator for its use as a prophylactic-therapeutic agent against obesity-related complications.